The On-Again, Off-Again Diet That Works

Nuala Byrne, PhD, head of the University of Tasmania School of Health Sciences, researcher and coauthor of the study “Intermittent Energy Restriction Improves Weight Loss Efficiency in Obese Men: the MATADOR Study,” published in International Journal of Obesity.

Published Date: April 23, 2018

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Do you feel that on-again, off-again dieting has become a way of life…with no pounds lost despite all your hard work? According to a new study, a purposeful twist on behavior that you likely see as dieting failure could be the key to weight loss—and weight loss that sticks!

The concept is surprising and surprisingly simple: Instead of trying to stay on a restrictive diet for a long stretch of time, follow a two-week on, two-week off plan. Called intermittent dieting, it involves alternating between distinct periods of weight loss and weight maintenance, each tied to a certain number of calories (yes, there’s a slight catch—more on that below), until you reach your goal.

The study: Forty-seven obese men, ages 25 to 54, participated in a study done at the University of Tasmania. The researchers separated them into two groups of similar weight loss needs. Half dieted for 16 weeks straight, reducing their normal calorie intake by one third during that time, and then they stopped dieting. The other half dieted during 16 weeks, reducing their normal calorie intake by the same amount (one third)—but it wasn’t for 16 weeks straight. Instead, they dieted for two weeks, stopped dieting for two weeks, dieted again for two weeks, and kept repeating that pattern for a total of 30 weeks.

The results: After their 16 net weeks of dieting (spread out over 30 weeks), the intermittent dieters not only lost nearly 50% more weight than the continuous dieters did after their constant 16 weeks —they also lost more fat and were more successful at keeping weight off. The overall process was longer, but for the same 16 diet weeks both groups followed in total, the intermittent dieters saw better results. What’s more, when researchers checked in with participants six months after dieting ended, the intermittent dieters had kept off more of the lost weight—almost 18 pounds more net loss, on average, from the start of the diet—than the continuous dieters. The researchers are currently testing the same intermittent dieting method on women, to see if it will work as well.

Now, before you stock up on ice cream and chocolate syrup for your next “two weeks off,” know that the two-week diet breaks aren’t meant to be a free-for-all—that’s what causes true yo-yo dieting—but rather a careful maintenance period. During their off weeks, study participants divided maintenance calories according to typical dietary guidelines—25% to 30% of calories came from fat, 15% to 20% from protein, and 50% to 60% from carbohydrates…and just enough calories to maintain their weight—meaning that the number of calories eaten was the same as calories burned, explained lead researcher Nuala Byrne, PhD.

But even so, how could going off and on a diet lead to greater weight loss and fat loss than continuously dieting?

The body’s metabolic processes and the human psyche both play a role. Even if you follow a conventional diet to the letter, the act of dieting alters a series of biological processes in your body, leading to slower weight loss over time and even potential weight gain. Simply put, your metabolism starts to work against you when you’re on a diet. This is because calorie restriction causes what Dr. Byrne referred to as the “famine reaction,” a natural survival mechanism to slow weight loss when your food supply is reduced, left over from the hunter-gatherer days. Your metabolism overrides your own intentions, slowing down to conserve energy by burning fewer calories and storing food as fat because it thinks you’re being starved by forces beyond your control.

The famine reaction can also result in an increased appetite—that explains why you might be disproportionately hungry when on a diet. But by taking a dieting hiatus every two weeks, you outsmart your body and prevent metabolism slowdown and everything that goes with it.

Another plus: Trying to stick to a strict diet—with no end in sight—is also mentally taxing. Taking a diet break every two weeks gives your mind a break from the stress of calorie restriction.

Here’s how make a two-week-on, two-week-off diet work for you:

Do the math. If you want to give this plan a go, your first step is to calculate how many calories your body needs to maintain your current weight, your daily “maintenance number”—and then reduce that number by one-third for the two-week periods you’ll be dieting, Dr. Byrne said. Then, for each two-week break from dieting, increase your calories to your maintenance number minus 100 or so calories (to account for the weight loss of the previous two diet weeks). Keep repeating the cycle. The NIH provides a free body-weight planner that will figure it out for you.

Add exercise. The study didn’t measure physical activity, but dieters tend to do less physical movement across the day—such as walking and doing chores—than non-dieters, noted Dr. Byrne. Being more active could enhance results.

Keep a food journal. As with any diet, you might feel hungry and experience food cravings during each two weeks of calorie restriction. Logging these cravings can help you notice patterns, such as at what times of the day they normally occur, so that you can set aside some of your calories for then or even restructure your meals at these times when appropriate.

Up your protein. Although more research is needed on this phenomenon, Dr. Byrne said it’s possible that increasing one’s intake of protein above the USDA recommended daily allowance of roughly 48 grams for women and 68 grams for men during calorie-restriction weeks could help with weight loss. In general, high-protein foods take more work to digest and metabolize than carbohydrates, which means it takes more calories for your body to process them…and there will be more time before you’re hungry again. Healthful protein sources include eggs, nuts, fish and lean meats.